U.S. Pat. No. 3,999,837 discloses a fiber optic connector which comprises a housing member and ferrule members terminated onto exposed ends of fiber optic transmission members. The housing member has a profiled bore including a center cylindrical section and outer first and second identically-shaped sections of different diameters. The ferrule members have cylindrical nose sections that tightly fit into the cylindrical section of the housing, tapered sections that engage the outer first and second sections, and annular shoulders that engage rearwardly facing surfaces of the housing member. Coupling members on the ferrule members are coupled to the housing member securing the ferrule members in the profiled bore with the cylindrical section applying radial compressive forces to the cylindrical nose sections thereby axially aligning the fiber optic transmission members and the annular shoulders engage the surfaces of the housing member limiting movement of the ferrule members into the profiled bore, positioning the front surfaces of the ferrule members adjacent each other and minimizing misalignment of the fiber optic transmission members when lateral forces are applied to the ferrule members.
When the annular shoulders of the ferrule members do not engage the axial surfaces of the housing member, lateral forces can cause misalignment of the fiber optic transmission members. Misalignment of single mode and multimode fibers can result in signal loss or degradation.